Methimazole (MMI)-induced acute pancreatitis is very rare but severe adverse reaction. A 51-yr-old male developed a high fever, chills, and abdominal pain, two weeks after commencement on MMI for the treatment of Graves' disease. There was no evidence of agranulocytosis, and fever subsided soon after stopping MMI treatment. However, 5 hr after taking an additional dose of MMI, abdominal pain and fever developed again. His symptoms, biochemical, and imaging studies were compatible with acute pancreatitis. After withdrawal of MMI, he showed clinical improvement. This is the first case of MMI-induced acute pancreatitis in Korea. Clinicians should be aware of the rare but possible MMI-induced pancreatitis in patients complaining of fever and abdominal pain.Graphical Abstract